closed angle is 45 degrees, the amount of bend is
180 minus 45 or 135 degrees. See figure 4-31.
· Open angle. An angle that is more than
90 degrees when measured between legs or less
than 90 degrees when the amount of bend is
· Flange. The shorter part of a formed angle--the
opposite of leg. If each side of the angle is the
same length, then each is known as a leg.
· Flat. The flat portion, or flat, of a part is that
portion not included in the bend. It is equal to the
base measurement minus the setback.
· K number. A K number is one of 179 numbers on
the K chart that corresponds to one of the angles
between 0 and 180 degrees to which metal can
be bent. When metal is to be bent to any angle
other than 90 degrees (K number of 1.0), the
corresponding K number is selected from the
chart and multiplied by the sum of the radius and
the thickness of the metal. The product is the
amount of setback for the bend.
· Leg. The longer part of a formed angle.
· Bend line. The bend line (also called the brake or
Figure 4-32.--Locating bend lines in a brake.
sight line) is the layout line on the metal being
formed that is set even with the nose of the
· Mold line. The line formed by extending the
brake, and it serves as a guide in bending the
work. Before forming a bend, the metalsmith
outside surfaces of the leg and the flange. (An
must decide which end of the material can be
imaginary point from which real base
most conveniently inserted in the brake. The
measurements are provided on drawings.)
bend line is then measured and marked with a
· Base measurement. The base measurement is
soft-lead pencil from the bend tangent line
the outside dimension of a formed part. Base
closest to the end that is to be placed under the
measurement will be given on the drawing or
brake. This measurement should be equal to the
blueprint, or it may be obtained from the original
radius of the bend. The metal is then inserted in
the brake so that the nose of the brake will fall
· Radius. The radius (R) of the bend is always to
directly over the bend line. See figure 4-32.
the inside of the metal being formed unless
· Bend tangent line. The line at which the metal
otherwise stated. The minimum allowable radius
starts to bend and the line at which the metal
for bending a given type and thickness of
stops curving. All the space between the bend
material should always be determined before
tangent lines is the bend allowance.
you proceed with any bend allowance
· Setback. The setback (SB) is the distance from
the bend tangent line to the mold point. In a
90-degree bend, SB = R + T (radius of the bend
plus thickness of the metal). The setback
dimension must be determined prior to making
the bend because setback is used in determining
the location of the beginning bend tangent line.
Figure 4-31.--Open and closed angles.